Abstract

The antifolate edatrexate has shown moderate activity against cancers of the head and neck and non-small cell lung cancer, as has cisplatin. Edatrexate demonstrates synergy with cisplatin in transplanted tumor models. This Phase I study was designed to evaluate two schedules of administration of cisplatin in combination with escalating doses of edatrexate, in a population consisting mainly of patients with these two cancers. The starting dose of edatrexate was 40 mg/m2. Dose escalation was to occur in 10-mg/m2 increments; the planned maximum dose level for study was 80 mg/m2. A total of 39 patients were registered. Eleven were treated on schedule A: cisplatin 120 mg/m2 every 4 weeks, and edatrexate weekly. Twenty-eight patients were assigned to schedule B: cisplatin 60 mg/m2 and edatrexate, both given every 2 weeks. On schedule A, the maximum tolerated dose of weekly edatrexate was 40 mg/m2, with dose-limiting toxicities of leukopenia, mucositis, and renal insufficiency. On schedule B, the maximum tolerated dose of biweekly edatrexate was 80 mg/m2, with leukopenia and mucositis as dose limiting. For schedule A, pharmacokinetic studies suggested a possible effect of cisplatin on the day 8 clearance of edatrexate. Studies on patients on schedule B did not show a clear effect of cisplatin on the day 15 edatrexate clearance. On schedule A, 5 of 9 evaluable patients had major responses (1 complete); whereas on schedule B, 8 of 25 patients had major responses (1 complete). Responses were seen in both head and neck and non-small cell lung cancer patients. For Phase II studies, use of cisplatin 60 mg/m2 and edatrexate 80 mg/m2, both given biweekly, is recommended.

INTRODUCTION

Edatrexate (10-ethyl-10-deazaaminopterin) is a second-generation antifolate that has been shown in murine tumor models and human tumor xenografts to have greater antitumor activity than its parent compound methotrexate (1)
. Proposed mechanisms to account for the improved therapeutic index of edatrexate include increased membrane transport and uptake into sensitive tumor cells compared with normal cells, and increased polyglutamation leading to greater intracellular accumulation and retention. Phase I studies of single-agent edatrexate led to a recommended dose for use in Phase II trials of 80 mg/m2 when given weekly (2)
. At this dose and schedule, the dose-limiting toxicity was mucositis. Objective responses were seen in patients with head and neck cancer, NSCLC,3
and breast cancer. As a single agent, the plasma pharmacokinetics of edatrexate are similar to those of methotrexate. Like methotrexate, edatrexate is subject to renal tubular secretion. Phase II trials of weekly edatrexate at 80 mg/m2 in patients with previously untreated NSCLC have revealed response rates of 10–32% (3)
. Edatrexate is an active agent in cancers of the head and neck, with response rates comparable with those of methotrexate (4)
.

Cisplatin is active in NSCLC and cancers of the head and neck. Standard dosing of cisplatin is 75–120 mg/m2 given as a bolus every 3–4 weeks. Although less commonly studied, cisplatin in divided doses can be administered biweekly with efficacy and acceptable toxicity (5)
. Cisplatin as a single agent causes little myelosuppression or mucositis. Preclinical studies in mice have found that the combination of edatrexate with cisplatin led to therapeutic activity which was greater than that obtained with each drug alone. (6, 7)
. Furthermore, the degree of synergism seen is greater than that observed between cisplatin and methotrexate. The synergism is schedule dependent, requiring that exposure to edatrexate occur prior to exposure to cisplatin (7)
. Synergism was still demonstrable after a 24-h interval between exposure to edatrexate and cisplatin.

Given the superior activity of edatrexate over methotrexate in preclinical studies, the antitumor activity against NSCLC and head and neck cancer seen in Phase I and II trials, the preclinical synergy seen between edatrexate and cisplatin, and the nonoverlapping toxicity profiles, we initiated this Phase I trial. Because of the synergy, it was deemed necessary to examine different schedules of administration of cisplatin in combination with edatrexate, given that different patterns of toxicity and efficacy may arise. This communication reports the results obtained from a Phase I trial performed at the Memorial Sloan-Kettering Cancer Center.

There has been a renewed interest in studying antifolates, including edatrexate, especially in combination with other agents. Encouraging results have recently been reported for the combination of edatrexate and paclitaxel (8, 9)
, where synergy was also seen preclinically (10)
. Recently published data suggest that edatrexate may be one of the most active single agents against mesothelioma (11)
. This class of agents continues to expand, with promising new agents such as MTA (12)
and PDX (13)
. Observations made during this study of edatrexate in combination with cisplatin may have relevance to the study of these newer agents.

PATIENTS AND METHODS

Patient Eligibility.

Adults with a Karnofsky performance status of ≥60% who had a histologically proven advanced, incurable solid tumor, and for whom no therapy with a greater likelihood of benefit was available, were enrolled. An interval of at least 3 weeks must have elapsed between any prior radiotherapy or chemotherapy. Previous chemotherapy must not have included cisplatin or methotrexate. After enrollment of the first four patients, the protocol was amended to require patients to be chemotherapy naive. Patients with extensive irradiation of major bone marrow-bearing areas (e.g., pelvic irradiation) were excluded. Patients were required to have adequate bone marrow (peripheral leukocyte count ≥4,000/mm3 and platelet count of ≥150,000/mm3), hepatic (bilirubin ≤1.5 mg/dl) and renal (creatinine clearance ≥55 ml/min) function. Patients with clinically significant third-space fluid accumulations (requiring paracentesis or thoracentesis) were excluded. Measurable disease was not mandatory. All patients provided signed informed consent. This trial was reviewed and approved by the Institutional Review Board of the Memorial Sloan-Kettering Cancer Center.

Treatment Plan.

Initially, it was planned to study the combination of cisplatin and escalating doses of weekly edatrexate using two different schedules (A and A1). In both, edatrexate was to be given weekly. Because edatrexate is partially cleared renally and due to the preclinical synergy data, edatrexate was administered 24 h prior to cisplatin. On schedule A, cisplatin 120 mg/m2 was administered on day 2, with a 28-day cycle (days 2, 30, 58, and so on). On schedule A1, cisplatin 40 mg/m2 was to be administered weekly for 3 of 4 weeks on a 28-day cycle (days 2, 9, 16, 30, 37, and so on). Accrual to schedule A was to be completed prior to initiating accrual to schedule A1. As the trial continued, however, it became apparent that administration of weekly edatrexate for more than one cycle was not possible, with the appearance of cumulative fatigue, mucositis, and neutropenia. No patients were accrued to schedule A1, and the protocol was amended to study the administration of both cisplatin and edatrexate on an every-other-week schedule (schedule B: edatrexate on days 1 and 15; cisplatin 60 mg/m2 on days 2 and 16). For both schedule A and schedule B, a cycle was considered to be 4 weeks of treatment. Fig. 1⇓
schematically illustrates the two schedules studied.

In both schedules, the starting dose of edatrexate was 40 mg/m2. Toxicity was assessed by the National Cancer Institute Common Toxicity Criteria scale (Bethesda, MD). The MTD was determined based on the toxicity seen in the first cycle of treatment. The MTD was considered to have been reached when grade 3 or greater toxicity was seen in two of six patients, or when grade 2 toxicity was seen in five or more of six patients.

It was planned to enroll three patients at each dose level, with expansion to six patients if grade 2 toxicity was seen in three patients or grade 3 or greater toxicity was seen in one person. Dose escalation was permitted if grade 3 toxicity was seen in no more than one of six patients at a given dose level or if grade 2 toxicity was seen in no more than two-thirds of patients. Dose escalation of edatrexate was to be in increments of 10 mg/m2. Escalation in individual patients was not permitted. On the basis of the results of the Phase I trial of edatrexate as a single agent, the highest dose level planned for study was 80 mg/m2. A minimum of six patients were to be studied at the MTD. A patient was required to have completed a full 4-week course (one cycle) to be considered as having received an adequate trial to evaluate the dose-finding aspects of this study. If patients were taken off study before receiving a full cycle of therapy, their toxicity data were included, but enrollment of an additional patient at that dose level was required.

Edatrexate was supplied by the National Cancer Institute as a lyophilized sterile powder in 50-mg ampuls. The drug was brought into solution by adding 4 ml of sterile normal saline, to achieve a concentration of 12.5 mg/ml edatrexate. The total dose of edatrexate was diluted in 50 ml of sterile normal saline and administered as a short i.v. infusion through the side arm of a freely running i.v. line during 20–30 min. Cisplatin was administered in a standard manner as an i.v. bolus through the side port of a freely running i.v. line. Hydration was given i.v. before and after cisplatin administration, and a mannitol bolus preceded the cisplatin. Those patients receiving the higher dose of cisplatin on schedule A also received an infusion of mannitol for 6 h after cisplatin administration. All patients were premedicated with standard antiemetics prior to cisplatin administration.

Doses of edatrexate and/or cisplatin were attenuated or held for toxicity observed on the day of therapy, as shown in Table 1⇓
. If a treatment was held, patients were evaluated weekly and treated as soon as resolution of their toxicities permitted. For grade 3 or 4 mucositis, all subsequent doses of edatrexate were reduced by 25 or 50%, respectively. The occurrence of neutropenic fever led to a reduction of all subsequent edatrexate doses by 25%. If any of these events occurred during the first cycle of therapy, they were considered as dose-limiting toxicities for purposes of defining the MTD.

At study entry, all patients had a complete history and physical examination, a complete blood count, a biochemical profile, and a 12-h creatinine clearance. Patients were seen weekly during cycle 1 and then every 2 weeks while on study. A complete blood count was repeated prior to each dose of edatrexate, and a 12-h creatinine clearance was required prior to administration of each dose of cisplatin. Although the determination of tumor response was not a primary objective of this Phase I study, in those with measurable or evaluable indicator lesions, assessment for response was to be performed by physical examination (where possible) every 4 weeks, and by appropriate imaging every 8 weeks. Standard criteria for response were used (14)
. For those with evaluable but not measurable indicator lesions, patients were considered to have improved if there had been a definite decrease in the size of the evaluable lesions for a minimum of 4 weeks, as agreed upon by two observers, without the appearance of new lesions (15)
. Radiographic responses were adjudicated by a reference radiologist. Responding patients could remain on therapy in the absence of unacceptable toxicity. Patients with progressive disease, and those in whom no evidence of response was seen after two cycles, were taken off study.

Pharmacokinetic Studies.

Pharmacokinetic studies were conducted with the first (day 1) and second (day 8 or 15, depending on treatment schedule) doses of edatrexate. Five ml of heparinized blood samples were obtained at the following times: preinfusion; after infusion (time 0); and at 5, 10, 15, 30, 45, 60 and 90 min and 2, 4, 6, 8, 12, 24, 30, 48, and 72 h postinfusion. It was planned to study three patients at the first edatrexate dose level and three patients at the proposed Phase II dose level.

Analytical Methods.

Edatrexate and its 7-hydroxy metabolites were measured using a HPLC assay with an Econosphere C18 column and an eluent consisting of 17% acetonitrile with 50 mm potassium phosphate (pH 7), with a flow rate of 1 ml/min. Edatrexate was detected by fluorescence with an excitation wavelength of 375 nm and an emission wavelength of 460 nm. The retention time for plasma was 5 min. The detection limit was 2 ng/ml. The full HPLC extraction procedure has been described (16)
.

Pharmacokinetic Calculations.

The AUC0→∞ was calculated using the trapezoid rule from time zero to the last measured time point and then extrapolated to infinity using the slope of the linear regression line through the terminal elimination phase via the PHARM/PCS version 4.2 software. Total body clearance of edatrexate was calculated from AUC using the formula, Clearance = (Edatrexate dose)/AUC.

Statistical Analysis.

All analyses were performed using the S-Plus software package (Mathsoft, Inc., Seattle, WA).

RESULTS

Patient Characteristics.

Thirty-nine patients were registered on this trial, 11 to schedule A and 28 to schedule B. Their characteristics are summarized in Table 2⇓
. Thirty-six had either squamous cell head and neck cancer (n = 18) or NSCLC (n = 18). Two patients on schedule B were registered but withdrew consent and were never treated, leaving 37 patients who received at least some treatment and are thus assessable for toxicity. These 37 patients remained on study for a total of 124 four-week cycles of therapy, with a median of 2 per patient (range, 0.5–20 cycles). The median number of cycles on therapy for patients assigned weekly edatrexate was 1 (range, 0.5–14), whereas for those assigned biweekly treatment, it was 2 (range, 0.5–20). On schedule A, 5 of 11 (45%) completed 2 or more cycles of therapy, whereas on schedule B, 20 of 26 (77%) remained on study for at least 2 cycles. Of the 37 treated patients, 3 were not evaluable for response (2 on schedule A, 1 on schedule B) because they did not complete 1 full cycle of therapy. Reasons for failure to complete one full cycle of therapy were the development of severe myelosuppression after the first infusions of cisplatin and edatrexate (one patient) and the development of intercurrent illness unrelated to therapy (two patients).

Schedule A Toxicity.

Table 3⇓
summarizes the number of patients treated at each dosage level and the severity and incidence of leukopenia, thrombocytopenia, mucositis, renal insufficiency, nausea, and fatigue seen during cycle 1 on schedule A; it includes a column that highlights the highest grade of toxicity of any type seen in each patient at each dose level studied. Table 4⇓
summarizes the highest grade of these toxicities recorded at any time during treatment. The toxicities listed are those for which severity of grade 3 or higher were recorded.

Highest National Cancer Institute grade toxicity observed at any time on therapy, schedule A

Of the first four patients enrolled to schedule A, two had received prior chemotherapy. Both these patients developed grade 4 myelosuppression with cycle 1 of therapy. The protocol was then amended to enroll only chemotherapy-naive patients. Three subsequent patients did not have any toxicity of grade 3 or greater with cycle 1 of therapy, permitting dose escalation. However, during the first cycle at 50 mg/m2, grade 3 mucositis and grade 4 leukopenia (one patient) and grade 4 fatigue and grade 3 elevation of creatinine (one patient) were seen. Thus, 40 mg/m2 was declared the MTD of edatrexate on this schedule, and two additional patients were enrolled at that dose level to further define toxicities. Dose-limiting toxicities were leukopenia, thrombocytopenia, mucositis, and renal insufficiency. Nausea was the only other toxicity that occurred with a severity greater than grade 2, with 3 of 11 patients experiencing grade 3 nausea at some point while on therapy. All episodes of nausea were thought to be related to cisplatin. One episode of grade 2 skin rash was seen. Other toxicities related to treatment seen on schedule A included ototoxicity and vomiting. These were never greater than grade 2 in severity.

Two patients were withdrawn from the study prior to the completion of cycle 1 of therapy because of profound myelosuppression (one patient who had received prior chemotherapy) and an intercurrent upper gastrointestinal hemorrhage requiring hospitalization and transfusion (one patient). Of the 9 patients who completed the first cycle of therapy, only 4 received all doses of edatrexate planned for cycle 1; 29 of 36 (81%) of planned edatrexate doses were delivered. Omissions were required due to mucositis, leukopenia, and fatigue, none of which was dose limiting in patients receiving 40 mg/m2. Only 5 of 11 patients (45%) completed 2 or more cycles of therapy. Reasons for failure to complete 2 cycles were toxicity (n = 2), intercurrent illness (n = 1), progression of disease (n = 2), and patient’s desire to decline any further anticancer therapy (n = 1). In patients on schedule A receiving weekly edatrexate who continued on therapy for more than one cycle, cumulative toxicities became apparent with increasing incidence and severity of mucositis and fatigue (Table 4)⇓
, and more reductions or omissions of scheduled edatrexate doses were required to ameliorate toxicity. During cycle 2, delivery of edatrexate to those 5 patients decreased to 11 of 20 (55%) planned doses; whereas in cycle 3, edatrexate delivery to 4 patients was 7 of 16 (44%). At the MTD the mean delivered dose intensities during cycles 2 and 3 were 22 and 20 mg/m2/week. No patient who continued therapy for more than one cycle received the full doses of edatrexate planned by the protocol. A responding patient with adenocarcinoma of unknown primary received edatrexate biweekly after the second cycle because of an inability to tolerate weekly administration, and continued on study for 12 months. A patient who had received cycle 1 of therapy without hematological toxicity died from polymicrobial septicemia during cycle 5, in the setting of grade 4 neutropenia and thrombocytopenia.

Schedule B Toxicity.

Table 5⇓
summarizes the number of patients treated at each dosage level of schedule B and the severity and incidence of adverse effects seen during cycle 1; it includes a column that highlights the highest grade of toxicity of any type seen in each patient at each dose level studied. Table 6⇓
summarizes the highest grade of these toxicities recorded. The toxicities listed are those for which severities of grade 3 or higher were observed.

Highest National Cancer Institute grade toxicity observed at any time on therapy, schedule B

Lower doses of edatrexate on schedule B were well tolerated. One patient at the 70-mg/m2 dose level had a fatal nonhemorrhagic stroke during cycle 1 of therapy, in the setting of grade 3 thrombocytopenia, grade 4 leukopenia and grade 3 mucositis. This dose level was expanded, and 5 other patients tolerated cycle 1 of therapy without grade 3 or greater toxicity, permitting dose escalation. Because 80 mg/m2 was the maximum dose planned for study, this level was expanded to nine patients when two patients with grade 3 toxicity (one patient with leukopenia and mucositis, one with mucositis and nausea) were observed in the first six patients enrolled. There were no other grade 3 or greater toxicities observed during cycle 1 at 80 mg/m2. The MTD of edatrexate on schedule B was 80 mg/m2. Dose-limiting toxicities were leukopenia and mucositis.

Only 6 of 26 (23%) patients enrolled on schedule B failed to complete 2 or more cycles of therapy [progression of disease (n = 5) and death from intercurrent illness (n = 1)]. In contrast to schedule A, 25 of 26 (96%) patients received all planned doses of cisplatin and edatrexate during cycle 1. In cycle 2, 35 of 40 (88%) planned doses of edatrexate were delivered to all patients. Eleven patients completed 3 or more cycles of therapy, and 20 of 22 (91%) planned doses of edatrexate during cycle 3 were delivered. Edatrexate delivery to those treated at the MTD, 80 mg/m2, was comparable with that of all patients enrolled on schedule B. In these patients, the corresponding figures were 17 of 18 planned doses (94%) for cycle 1; 11 of 14 (79%) for cycle 2, and 9 of 10 (90%) for cycle 3. At 80 mg/m2, the mean delivered dose intensities of edatrexate during cycles 2 and 3 were 31 and 32 mg/m2/week. Although the differences between edatrexate dose intensity in those treated at the MTD of schedules A and B were not statistically significant (cycle 2, 22 versus 31 mg/m2/week, P = 0.128; cycle 3, 20 versus 32 mg/m2/week, P = 0.355 by Wilcoxon rank sum test), the number of patients was limited. In patients on schedule B who continued therapy for more than three cycles, there appeared cumulative toxicities of fatigue, leukopenia, and mucositis (Table 6)⇓
. This was most apparent at the higher edatrexate dose levels, particularly for leukopenia at 80 mg/m2, although these toxicities were never higher than grade 3 in severity. This led to an increased incidence of edatrexate and cisplatin dose reductions, omissions, and delays during the fourth and subsequent cycles. One patient at the 50-mg/m2 dose level developed grade 3 ototoxicity due to cisplatin during cycle 3. Cisplatin was discontinued, but because this patient was responding to therapy, edatrexate alone was continued for an additional 17 cycles, without undue toxicity.

Pharmacokinetics.

For schedule A, four patients at the 40-mg/m2 dose level were studied; whereas for schedule B, three patients at each of the 40-, 60-, and 80-mg/m2 dose levels were examined. These results are summarized in Table 7⇓
. There are incomplete data for two patients on schedule B. Edatrexate clearance varied widely and did not seem to correlate with dose level. There was interpatient variability in the peak levels of edatrexate at any given dose level. Mean AUC tended to increase with increasing doses of edatrexate. Studies in patients on schedule A suggest an effect of day 2 cisplatin on day 8 edatrexate pharmacokinetics, with a significant increase in AUC seen in all four patients. Mean AUC increased from 1307.0 ng/ml/h on day 1 to 2903.2 ng/ml/h on day 8 (change in mean, 1596.3 ng/ml/h; paired t test P = 0.03). Mean clearance dropped from 40.5 liters/h/m2 after day 1 edatrexate to 15.2 liters/h/m2 after day 8 dosing (P = 0.10). There was no clear effect of day 2 cisplatin seen, however, on day 15 edatrexate clearance in those patients studied on schedule B, with patients showing essentially unchanged clearance.

On schedule A, patient 2 had a day 1 edatrexate AUC roughly double that of the other patients. This patient suffered significant myelosuppression during cycle 1 of therapy; however, this patient had also received prior chemotherapy. No other correlation between edatrexate pharmacokinetic profile and toxicity was observed on either schedule.

Responses.

The major objective responses are summarized in Table 8⇓
. On schedule A, there were five major responses seen in nine evaluable patients (56%; 95% confidence interval, 23–88%). A complete response lasting 5 months was seen in a patient with a squamous carcinoma of the head and neck who had previously received surgery and radiotherapy and who was treated at a weekly edatrexate dose level of 50 mg/m2. The other major responses were maintained for 1.5 to 10 months. On schedule B, there were 8 major responses seen in 25 evaluable patients (32%; 95% confidence interval, 14–50%). Responses were seen at all dose levels. A complete response lasting 6 months was seen in a patient with a squamous carcinoma of the head and neck who had previously received surgery and radiotherapy and who was receiving edatrexate at 50 mg/m2 biweekly. The duration of the major responses ranged from 3 to 9 months, with one additional partial response maintained for 19 months. Because only three of the responders (patients 10, 11, and 21) had full pharmacokinetic studies, no conclusions can be drawn regarding the relationship between response and edatrexate clearance.

DISCUSSION

Edatrexate has documented activity against carcinoma of the breast (17, 18)
, head and neck cancer (4)
, and NSCLC (3)
. Furthermore, antifolates, including edatrexate and MTA, may be among the most active agents in malignant mesothelioma (11, 19, 20)
. This has sparked a renewed interest in this agent and this family of cytotoxics. At Memorial Sloan-Kettering Cancer Center, further modification of edatrexate, with the addition of a propargyl group at C10, has led to the discovery of a compound with enhanced preclinical activity (13)
. This compound, PDX, has completed Phase I testing and is now in Phase II testing, both as a single agent and in combination with paclitaxel and probenecid. The best way of administering these antifolates and of combining them with other cytotoxic agents needs to be determined. The experiences with each agent may assist with the development of newer antifolates. Cisplatin is an obvious agent to study in combination with antifolates given the documented preclinical synergy with methotrexate and edatrexate and its broad spectrum of antitumor activity.

The Phase I study of weekly single-agent edatrexate led to a recommended Phase II dose of 80 mg/m2 with dose escalation or reduction based on patient tolerance (2)
. Dose-limiting toxicity was mucositis, but the trial also suggested that, when given weekly, edatrexate becomes increasingly difficult to tolerate after a few doses and requires interruption of the schedule and/or dose reduction. The mean dose administered in that trial was 60 mg/m2/week. A Phase II trial of edatrexate at 80 mg/m2/week in metastatic breast cancer also found that the mean delivered dose intensity was 57 mg/m2/week (17)
. Identical results were obtained in a trial of weekly edatrexate in patients with metastatic melanoma (21)
. Treatment delays and dose reductions were also common in other Phase II trials using weekly edatrexate (18, 22)
. In a study of patients with advanced head and neck cancer (4)
, the weekly dose of edatrexate was decreased from 80 mg/m2 to 70 mg/m2 during the trial because of toxicity.

With the recognition that administration of weekly edatrexate leads to significant toxicity and a subsequent inability to deliver planned doses, attempts have been made to modify the schedule of administration. Perez et al.(23)
performed a Phase I study of biweekly edatrexate and found less mucositis despite increased dose intensity. Others have studied an induction period of weekly edatrexate for 5 weeks, followed by biweekly administration (24)
, and found this to be better tolerated. The initial intention of that study was to administer edatrexate weekly; the protocol was amended after the accrual of nine patients to biweekly administration after the 5-week induction period because of toxicity. In a Phase I study of the antifolate PDX, biweekly administration was better tolerated and permitted greater dose escalation, leading to a dose intensity 2.5-fold higher than that obtained with weekly dosing (25)
.

The results of this current Phase I study confirm that a weekly schedule of edatrexate, in combination with monthly cisplatin, is not optimal. The dose could not be escalated above 40 mg/m2/week. The median number of cycles delivered was only 1; in those who continued therapy, no patient received the amount of edatrexate planned by the protocol because of the appearance of cumulative toxicities of mucositis, leukopenia, and fatigue. In cycles 2 and 3, only 55 and 44% of planned edatrexate doses were delivered. In contrast, treatment with edatrexate and cisplatin, both given on a biweekly schedule, was better tolerated, as evidenced by the higher maximum tolerated dose of edatrexate and the increased median number of cycles delivered. There was greater adherence to the doses planned in the protocol, with 88 and 91% of edatrexate doses delivered in cycles 2 and 3, suggesting a delay in onset of cumulative toxicities. As a result, although planned dose-intensity of edatrexate was the same in both schedules, delivered dose intensity in cycles 2 and 3 was higher with biweekly administration. Although the difference in drug delivery at the MTD of both schedules was not statistically significant, likely due to small patient numbers, the toxicity difference between the two arms was clinically significant.

The toxicities seen in this trial (mucositis, myelosuppression, fatigue, nausea) were predicted from experience with cisplatin and single-agent edatrexate. No unexpected toxicities were seen. Although weekly edatrexate has been associated with a characteristic skin rash (26)
, it was uncommon in this trial. No pulmonary or hepatobiliary toxicity attributable to edatrexate was observed. There was no clear relationship between prior radiation therapy to the head and neck and the development of mucositis. On schedule A, the two patients who developed grade 3 mucositis had both previously received radiation to the head and neck, compared with only one of four patients who developed grade 3 mucositis on schedule B. Two of the first four patients enrolled to schedule A had been heavily pretreated with chemotherapy, and both suffered profound myelosuppression during cycle 1 of therapy. Caution is indicated in administering this regimen to pretreated patients. Others (27)
have suggested that when weekly edatrexate is given by 2-min bolus, a 1-h plasma edatrexate concentration >3 mm is modestly predictive of hematological toxicity and the need to dose reduce. In our trial, edatrexate was infused during 20 to 30 min; thus, we cannot confirm or refute this finding. Of those studied on schedule A, patient 2, who had a day 1 AUC roughly double that of the other patients, developed grade 4 myelosuppression (see Table 7⇓
). However, this patient differed from the others in that he had received previous chemotherapy; and because the total number of patients studied is small, no conclusions can be drawn regarding the relationship between weekly edatrexate pharmacokinetics and toxicity. Likewise, there was no clear relationship seen on schedule B between toxicity and pharmacokinetic profile.

Previous studies have shown that there is wide interpatient variability in edatrexate pharmacokinetics (2, 27)
. However, there is no significant alteration in pharmacokinetic profile in individual patients when two sequential weekly doses are administered (2, 28)
. On schedule A, cisplatin appeared to have impaired the clearance of day 8 edatrexate; this may have contributed to the increased toxicity seen with this schedule. In contrast, administration of a lower dose of cisplatin on a biweekly schedule did not impact the clearance of the next dose of edatrexate, given on day 15. Possible explanations for this include a lesser degree of renal tubular dysfunction arising from the lower dose of cisplatin, and/or the increased interval between administration of cisplatin and the subsequent dose of edatrexate, which allows for resolution of subclinical tubular dysfunction. This may have implications for the design of future trials combining a water-soluble, renally excreted antifolate with cisplatin.

The relative contribution of altering both cisplatin and edatrexate scheduling to the improved tolerance of the regimen is unclear. Because the pharmacokinetics and pattern of toxicity of edatrexate are similar to that of methotrexate, it is likely that increasing the interval between doses will improve tolerance. Methotrexate tolerance is improved by increasing the interval between doses, permitting mucositis to fully resolve prior to subsequent doses. The divided dosing of cisplatin likely explains the lower incidence and severity of nausea seen on schedule B. Significant nephrotoxicity was also not seen on this schedule, likely reflecting the divided dosing of cisplatin, in that nephrotoxicity is dose related (29)
. As renal function declines after repeated cisplatin administration, impaired renal clearance of edatrexate may develop. This series of events may contribute to and explain the appearance of cumulative toxicities.

It is unclear whether the separation of the administration of edatrexate and cisplatin by 24 h, as was done in the current trial, is necessary to avoid alterations in edatrexate pharmacokinetics, minimize toxicity, and obtain synergy between the agents. It has been shown that provided exposure to edatrexate precedes that of cisplatin, synergy in preclinical models can be documented with a interval of as little as 1 h (7)
. Investigators have found that cisplatin at 50 mg/m2 did not impact the clearance of a dose of methotrexate given the same day, when compared with the clearance of methotrexate given as a single agent 2 weeks prior (30)
. Thodtmann et al.(20)
performed a Phase I trial of MTA in combination with cisplatin and found that giving both drugs on day 1 led to less toxicity than delaying the administration of cisplatin to day 2. Our study has shown that on a biweekly schedule, cisplatin has no effect on the clearance of the subsequent dose of edatrexate. This would suggest that edatrexate and cisplatin at this dose could be administered on the same day without influencing the clearance of either that day’s or the next dose of edatrexate, increasing the ease of delivery of the regimen.

The tolerability of the regimen might be further enhanced in ways other than altering the schedule of administration. It has been suggested that because of the short initial half-life of edatrexate, ice-chip oral cryotherapy, in the manner described for 5-fluorouracil, may reduce the incidence and severity of mucositis (31)
. This may not be feasible in some patients, such as those with significant anatomical abnormalities related to head and neck cancer; furthermore, diminishing drug delivery to the area exposed to ice chips could theoretically impact the efficacy of treatment of head and neck cancer. The addition of leucovorin, 15 mg p.o. every 6 h for 4 doses starting 24 h after edatrexate administration, has also been purported to decrease edatrexate toxicity, especially mucositis (11)
, (32)
; however, it is possible that leucovorin may decrease the antitumor activity of edatrexate (11)
. Fatigue, a commonly observed cumulative toxicity of edatrexate and especially cisplatin, could be partially due to chemotherapy-induced anemia and might be ameliorated with the use of erythropoietin therapy (33)
.

Others have studied the combination of edatrexate with platinum compounds. Preclinical synergy with carboplatin has been demonstrated (34)
. Edelman et al.(31)
performed a Phase I trial, in previously untreated patients with a variety of solid tumors, of edatrexate in combination with carboplatin, 350 mg/m2 every 4 weeks. Edatrexate was given weekly for five doses and then biweekly. With the use of ice-chip oral cryotherapy, this regimen was well tolerated, with an ability to escalate the edatrexate dose to 110 mg/m2. Although mucositis was commonly observed, no grade 4 mucositis was seen, and grade 3 mucositis occurred in only 15% of patients. Leukopenia was the dose-limiting toxicity; fatigue of any grade was seen in only 11 of 46 (24%) and was of grade 3 severity in only 1 patient. Major objective responses were observed in 12 patients (26%), including those with NSCLC (4 of 14) and cancer of the head and neck (2 of 6). This study supports the further study of biweekly edatrexate in combination with platinum compounds in these patients. The altered toxicity profile seen in this study compared with ours may reflect the use of ice-chip oral cryotherapy and the substitution of carboplatin for cisplatin. Lee et al.(35)
reported a trial of edatrexate in combination with cyclophosphamide and cisplatin in 32 patients with advanced NSCLC previously untreated with chemotherapy. Cisplatin and cyclophosphamide were given on day 1 and edatrexate was given on days 1 and 8 of a 21-day cycle. A 12.5% dose reduction of all agents was required after enrollment of the first 16 patients because of significant myelosuppression; with the reduced doses, there was a decrease in bone marrow toxicity, but also an apparent decrease in response rates (47 versus 27%). Despite the dose reduction, the administered doses of cyclophosphamide and cisplatin were not significantly different between the two groups, but there was a significant decrease in the mean dose of edatrexate delivered. The authors believe that this implies a steep dose-response relationship for edatrexate. If this were true, strategies, such as biweekly administration, that permit the delivery of higher individual doses and that could lead to higher dose intensity of edatrexate would be preferred.

Major responses, including complete responses, were seen with both schedules of administration in patients with cancers of the head and neck and NSCLC, showing encouraging activity for this two-drug combination and holding the promise of enhanced activity for the combination of PDX, MTA, and other antifolates with cisplatin. The lack of demonstrated superiority of single-agent weekly edatrexate over methotrexate should not discourage further study of edatrexate and related compounds on a biweekly schedule, which may be better tolerated and result in improved drug delivery. Except perhaps during a brief induction period, continuous weekly dosing may not be the preferred strategy for administering edatrexate. Furthermore, synergy has been shown for edatrexate in combination with several other cytotoxic agents, including cisplatin (6, 36)
and paclitaxel (10)
; in combination with cisplatin, the degree of synergism seen with edatrexate is greater than that shown with methotrexate. There remains the potential that edatrexate and related compounds given biweekly in combination with cisplatin or other agents may result in therapeutic gains with manageable toxicity.

Footnotes

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